Microalgal flour

ABSTRACT

The present invention relates to microalgal food products with acceptable sensory characteristics and methods of producing the food products. The flour can be produced by cultivating microalgal cells of a strain of Chlorella protothecoides under conditions of acceptable pH and dissolved oxygen to produce a desired amount of lipid. The microalgal cells can be lysed, heat-treated, washed and dried to produce a microalgal flour that can be incorporated into a variety of products.

CROSS-REFERENCE TO RELATED APPLICATION

This application claims priority under 35 U.S.C. § 119(e) to U.S. provisional application No. 61/757,534, filed Jan. 28, 2013, the entire contents of which is hereby incorporated by reference.

TECHNICAL FIELD

The present invention relates to microalgal food products with improved flavor and methods of producing the food products.

BACKGROUND

As the human population continues to increase, there is a growing need for additional food sources, particularly food sources that are inexpensive to produce but nutritious. Moreover, the current reliance on meat as the staple of many diets, at least in the most developed countries, contributes significantly to the release of greenhouse gases. There is a need for new foodstuffs that are less harmful to the environment to produce.

Requiring only “water and sunlight” to grow, algae have long been looked to as a potential source of food. While certain types of algae, primarily seaweed, do indeed provide important foodstuffs for human consumption, the promise of algae as a foodstuff has not been fully realized. Algal powders made with algae grown photosynthetically in outdoor ponds or photobioreactors are commercially available but have a deep green color (from the chlorophyll) and a strong, unpleasant taste. When formulated into food products or as nutritional supplements, these algal powders impart a visually unappealing green color to the food product or nutritional supplement and have unpleasant fish, seaweed or other flavors.

There are several species of algae that are used in foodstuffs today, most being macroalgae such as kelp, purple laver (Porphyra, used in nori), dulse (Palmaria palmate) and sea lettuce (Ulva lactuca). Microalgae, such as Spirulina (Arthrospira platensis) are grown commercially in open ponds (photosynthetically) for use as a nutritional supplement or incorporated in small amounts in smoothies or juice drinks (usually less than 0.5% w/w). Other microalgae, including some species of Chlorella are popular in Asian countries as a nutritional supplement.

Poor flavor is a major factor that has impeded the widespread adoption of microalgae in food. WO2010/12093 discloses methods of making and using microalgal biomass as a food. That reference discloses the growth of microalgae in the dark, to produce a microalgal biomass. However, further improvements in flavor of microalgal biomass should promote further adoption.

SUMMARY

The present invention relates to microalgal food products with acceptable sensory characteristics and methods of producing the food products. The flour can be produced by cultivating microalgal cells of a strain of Chlorella protothecoides under conditions of acceptable pH and dissolved oxygen to produce a desired amount of lipid. The microalgal cells can be lysed, heat-treated, washed and dried to produce a microalgal flour that can be incorporated into a variety of products.

In one embodiment of the present invention, a microalgal flour suitable for use in food is provided, the flour comprising microalgal cells of Chlorophyta, wherein analysis by SPME according to Example 4 and SBSE according to Example 5 to determine concentrations of the compounds of Example 6 relative to an internal standard, followed by analysis according to the procedure of Example 9 produces a flavor descriptor that falls within the ellipsoid of Example 8 defining 3 standard deviations relative to the positive flavor cluster corresponding to the closed circles in the graph of FIG. 2.

The aforementioned microalgal flour is obtainable in one embodiment of the present invention, by the process of cultivating a broth of cells of Chlorella protothecoides in the dark in the presence of glucose as a fixed carbon source with a starting pH of 6.8, while maintaining the dissolved oxygen level above 30%, subjecting the broth to a high-temperature-short-time process of 75° C. for 1 minute, harvesting the cells by centrifugation with a dilution of 6.4 fold in water, lysis of the cells by milling, adding an antioxidant, and drying using a spray-dry nozzle outputting to a moving belt.

BRIEF DESCRIPTION OF THE DRAWINGS

The features of the invention will be more readily understood by reference to the following detailed description, taken with reference to the accompanying drawing, in which:

FIG. 1 shows a flow diagram depicting a method of producing a food product in accordance with an embodiment of the present invention.

FIG. 2 is a graph showing the PCA analysis clustering discussed in Example 7.

DETAILED DESCRIPTION OF EMBODIMENTS OF THE INVENTION Definitions

In connection with a culture medium, “dissolved oxygen,” abbreviated as “DO” means the relative oxygenation of the culture medium as compared to the oxygenation of a culture medium that is in oxygen equilibrium with the atmosphere.

A “microalgal flour” is a dry, particulate composition, fit for human consumption, comprising cells of microalgae.

As used herein, an “off-flavor” means a flavor that a consumer would not expect and/or is undesired in a food, for example a baked food, such as a cake. Examples of off-flavors include flavors of cabbages or fish. Although specific flavors may be measured by modern analytical techniques such as Gas Chromatography-Mass Spectrometry (abbreviated as GC-MS), often the most convenient and effective tool for measuring off-flavors is a tasting panel comprised of humans. In connection with human perception of off flavors, these may be determined by a sensory panel of, for example, 10 people, where absence of a flavor or odor is established when 2 or fewer of the 10 people can detect the flavor, or by performing enough tests to establish statistical significance.

Overview

The present invention is rooted in the discovery that certain strains of microalgae can produce an appetizing biomass in terms of flavor, odor and color, when cultivated and processed under particular conditions. The improved flavor is believed to result not just from the absence of off-flavors but from the presence of desirable flavor compounds produced during cultivation and/or processing. In the Examples below, the microalgae is a strain of Chlorella protothecoides cultivated heterotrophically, in the dark, but could be another species of Chlorella or other species of Chlorophyta, provided that a non-green color can be produced via heterotrophic cultivation and careful processing such as by using the methods given below. By use of these techniques, the product may fall within the newly identified acceptability criterion disclosed here.

Human sensory panel data on multiple batches of microalgal flour was correlated with data from an extensive analysis of flavor and odor compounds of varying solubility in water to identify a clustering in flavor/odor space as represented by a principal component analysis. Thus, a microalgal flour that falls within the identified cluster has a high probability of being acceptable for human consumption.

FIG. 1 is a flow diagram of a process for producing microalgal flour having low amounts of off-flavors, in accordance with embodiments of the invention. The resulting flour may be incorporated into a variety of foods and beverages.

Production of Improved Microalgal Flour

Microalgae are cultured (step 105). It has been found that culturing the microalgae in the dark creates microalgal biomass having lower levels of off-flavors such as mushroom and cabbage or fish flavors; e.g., when microalgal flour dispersed in deionized water at 10% (w/v), and evaluated by a human sensory panel. Thus, in a preferred embodiment, the microalgae are cultured heterotrophically, in the dark on a fixed (i.e. non-CO₂) carbon source. While glucose was used in the examples below, other fixed carbon sources such as fructose, sucrose/fructose mixtures, or acetic acid/acetate may produce comparable results. The sugar concentration can be controlled by continuous feeding. Favorable results have been achieved with a glucose concentration of between 3 and 10 g/l. Suitable genera of microalgae include Chlorella and Protetheca. For example, Chlorella protothecoides, Prototheca moriformis or Prototheca zopfii may be used. Other species of Chlorella used for human nutrition, such as Chlorella protothecoides can also be grown and processed as disclosed here. Combinations of microalgal species or strains may also be used. Optionally, the microalgal cells are mutated and a strain selected to be substantially reduced in pigment that may change the color of a food product into which the biomass is incorporated. In the examples below, it was found that suitable flavor and no observable green color could be obtained from cells of Chlorella protothecoides. For example, the flour may comprise less than 200, 20, or 2 ppm of chlorophyll. In the examples below, the color was found to be yellow/gold, but could also be, for example, pale-yellow, off-white, or white depending on the strain and cultivation/processing conditions used.

The microalgae are cultured to a desired density and lipid concentration. The lipid concentration may be increased by culturing under nutrient-limiting and especially nitrogen-limiting conditions. In embodiments of the invention, culturing is performed under conditions of limiting nitrogen so that the microalgae reach 10-20%, 20-30% 40-50%, 40-60%, 30-70%, 35-75%, 50-60%, 60-70%, or 70-85% lipid, as measured by dry cell weight. In the exemplified embodiments, the microalgae comprise about 50% lipid. Elevated levels of lipid are especially useful in producing food products with improved fat and cholesterol profiles or improving the mouthfeel of such products. When a high lipid microalga is used to produce the flour, the stickiness of the lipid can be an impediment to forming a flour that is measurable and/or flowable. Alternately, cultivation under nitrogen-replete conditions can give a high-protein microalgal flour, such as flour can have, for example 5-20% or 10-18% lipid by dry cell weight. As described below, drying methods have been identified that give a flowable powder while retaining the desirable taste, odor and color characteristics.

The microalgae may be cultured in an opaque culture vessel. The microalgae may be cultured under aerobic conditions. Surprisingly, it has been found that increasing the oxygen level to 30% DO or more during heterotrophic culture of Chlorella protothecoides can result in a microalgal biomass having improved flavor. Variation of ±30% in DO (i.e., 30±9% DO) is contemplated. In addition, elevated oxygen (e.g., >40% DO, >50% DO, >60% DO, or 60-70% DO) during fermentation can result in a microalgal biomass having a white or off-white color with low amounts of off-flavors. Whiteness may be measured with a Hunter colorimeter. In an embodiment, the whiteness is greater than the whiteness of a control sample of microalgal biomass grown at about 30-40% DO. In a specific embodiment, the oxygen is elevated to about 60-70% dissolved oxygen. Increased oxygenation can be achieved, for example, by the introduction of purified oxygen.

The flavor may be improved by culturing the microalgae at a desired pH. For example, the pH could be from 4 to 9, or from 5 to 8. The pH may be controlled using buffering and/or pH monitoring with titration. If an acidic pH is used, the pH can be neutralized by adjusting to a pH of 6 to 8 or 6.5 to 7.8, or about 7; e.g., prior to drying to avoid astringent flavor. The final flour may be characterized by a pH of 5.5-8.5, 6.0-8.0, or 6.5-7.5 for a 1% w/v solution of flour in water.

After culturing, the microalgae are inactivated (step 110). Inactivation conditions are chosen to be sufficient to inactivate enzymes that produce off-flavors. These conditions may also kill the microalgae or stop growth of the microalgae and contaminating species, if any. It has been found that rigorous pasteurization (i.e., at high temperature and/or long times) can lead to undesirable flavor/odor, while treatment that is not rigorous enough also can lead to unacceptable flavor/odor. Thus, when pasteurization is used, a delicate balance must be struck. Experiments have shown that a high-temperature-short time pasteurization (“HTST”) treatment regime can be used to produce an acceptable microalgal biomass product. For example, the temperature of the treatment may be from 70° C. to 95° C., or 72° C. to 90° C., for from 10 to 180, 30 to 120, or 45 to 90 seconds. In one embodiment, microalgae are treated at 75° C. for 1 minute by flowing the cultured microalgal broth through a heat exchanger into a collection vessel. Cooling of the HTST output is preferred to avoid prolonged heating. Similar results should be obtainable by adjustment of both time and temperature. Delay prior to inactivation should be minimized so as to prevent the development of off-flavors, which are believed to be created by enzyme activity. Thus, in an embodiment of the present invention, the step of inactivating enzymes is performed without delay of a time sufficient to allow production in the microalgae of enzymatically developed off-flavors. Culture at an acidic pH may also allow for an even more gentle pasteurization to be used. For example, the microalgal cells can be cultured at a pH of from 5 to 6.5, followed by pasteurization at from about 60 to about 70° C. for 1 minute, and neutralization prior to drying.

To further improve flavor, the microalgal cells may be washed (step 115). Without wanting to be bound by theory, the washing may remove off-flavors. In addition, using an inactivation step prior to washing may permeabilize the cells or otherwise promote the removal of unwanted flavors or odors from the microalgal biomass. Washing may be performed by centrifugation, filtration, dialysis or other method known in the art. Optionally, the washing is performed with a volume of wash liquid (e.g., water or buffer) that is as great or greater than the volume of the microalgal cells (e.g., as measured by centrifugation). The volume of wash liquid may be twice the volume of the cells, or preferably, at least 3 times the volume of the cells. It was found that centrifugation in 6.4 times the cell volume gave a microalgal biomass with favorable flavor. Accordingly, in an embodiment of the present invention, the cells are washed with between 3 and 12 volumes of water. For these purposes, measurement of the cell volume is accomplished by dewatering the cells (i.e., removing them from the liquid growth medium). For example, the cells may be dewatered by centrifugation or filtration. Optionally, the washing step may be repeated one or more times.

Optionally, after washing, a preservative may be added (step 120). For example, sodium benzoate and/or potassium sorbate may be added as a bacteriostatic and fungistatic agent. Since sodium benzoate is more active under acidic conditions, the pH may be lowered as necessary. In that case, the pH can be raised later in the process to avoid an unwanted acidic flavor.

Optionally, the microalgal cells are then lysed (step 125). The lysis may be partial, or complete. For example, from 5% to 95% or a majority (>50%) of the cells may be lysed. Lysis may be especially desirable to release lipids in a high-lipid microalgae, where release of the lipids improves the quality or nutritional value of a food product into which the microalgal biomass is incorporated. Lysis may be accomplished with a bead mill, or any other suitable method known in the art. Optionally, a majority of the cells can be lysed. In one embodiment, about 30-75% of the microalgal cells are lysed. In another embodiment, about 30-75% of the microalgal cells are lysed and the microalgal cells have about 30-75% lipid by dry cell weight. In yet another embodiment, the microalgal cells are 60-90% lysed. This combination of parameters is believed to lead to a microalgal biomass that improves the mouthfeel, air-holding capacity or other functional parameters of a food into which it is integrated, while avoiding difficulties in drying or other processing steps that may be associated with highly lysed cells. In Example 3 below, the cells were lysed to about 80%.

Optionally, the biomass may be homogenized (step 130). For example, the suspension containing the cells and/or lysed cells may be forced through a narrow channel or orifice at elevated pressure (i.e., use of a high-pressure homogenizer). Other types of homogenizers such as blade or ultrasonic homogenizers may also be employed.

An antioxidant may be added to enhance the shelf life of the biomass (step 135). For example, tocopherols, BHA, BHT, rosemary extract, or other suitable food-grade antioxidants can be used. In addition to enhancement of shelf life, addition of antioxidant at the stage may prevent unwanted oxidation flavors from forming in the drying step. At this stage, addition of a base to raise the pH may prevent astringent flavors associated with a low pH if low pH conditions were used in upstream processes.

Prior to drying (e.g., after homogenization and before or after the optional addition of antioxidant), the microalgae can be held at elevated temperature for a period of time (140). Without wanting to be bound by theory, it is believed that this step promotes stability of the flavor, ensures inactivation of enzymes, and may promote the formation of positive flavors. For example, a suspension of lysed microalgae can be held at 70-85° for 1-6 minutes. In the Example 3 below for which acceptable sensory properties were obtained in the flour produced, this heating step was performed at 77° C. for 3 minutes. Comparable results may be obtained, for example, by heating at about 87° C. for about 90 seconds or about 67° C. for about 6 minutes.

The biomass is then dried (step 145). In one embodiment, in order to form a flour (a powder-like) substance, the biomass is spray dried. The spray drying may use, for example, a box-dryer, or a tall-form spray-dryer, a fluidized bed dryer, or a moving fluidized bed dryer (e.g., a FilterMat® spray dryer, GEA Process Engineering, Inc.). Example 3 describes conditions used for drying with a FilterMat drier.

The resulting flour may be measureable or flowable, even if high in lipid (e.g, 30-70 or 40-60% lipid by dry cell weight). In a specific embodiment, the flour has an aerated density of 0.30 to 0.50, a bulk density of 0.50 to 0.65, an oversize of 15-35% by weight at 2000 μm (i.e., % too large to pass through a 2000 μm sieve), 40-70% at 1400 μm and 1-20% at 800 μm, a wetability of 1-25 mm, and a surface area of 0.1 to 0.7 m²/g.

To test wetability:

-   -   introduce 500 ml of deionized water at 20° C. into a 600 ml         squat-form beaker (Fisherbrand FB 33114),     -   place 25 g of the microalgal flour powder uniformly at the         surface of the water, without mixing,     -   observe the behavior of the powder after 3 h of contact,     -   measure the height of the product that has penetrated the         surface of the water and settled at the bottom of the beaker.

The aerated bulk density is determined using a conventional method of measuring aerated bulk density, i.e. by measuring the mass of an empty container (g) of known volume, and by measuring the mass of the same container filled with the product to be tested.

-   -   The difference between the mass of the filled container and the         mass of the empty container, divided by the volume (ml) then         gives the value of the aerated bulk density.     -   For this test, the 100 ml container, the scoop used for filing         and the scraper used are supplied with the apparatus sold by the         company Hosokawa under the trademark Powder Tester type PTE.     -   To perform the measurement, the product is screened through a         sieve with apertures of 2000 μm (sold by SAULAS). The density is         measured on the product that is not retained on that screen.

The specific surface area is determined over the whole of the particle size distribution of the microalgal flour granules, e.g., by means of a Quantachrome specific surface area analyzer based on a test for absorption of nitrogen onto the surface of the product subjected to the analysis, carried out on a SA3100 apparatus from Beckmann Coulter, according to the technique described in the article BET Surface Area by Nitrogen Absorption by S. BRUNAUER et al. (Journal of American Chemical Society, 60, 309, 1938).

The microalgal flour is tested for acceptable flavor, color odor, and/or mouthfeel (step 150). For example, a human sensory panel may be employed and/or analytical technology such as headspace GC-MS, SPME, or SBSE. Optionally, the flavor may be evaluated to determine if it is grouped with or falls within boundaries associated with acceptable flavor determined by a prior sensory panel and/or analytical testing. The groupings/boundaries may be determined with the use of principal component analysis (PCA) (see Examples below). An acceptable lot may then be selected for packaging and future use.

After drying and optional testing, the biomass may undergo any further processing or packaging (step 155) needed to make a microalgal flour or a food product that incorporates the biomass. For example, to make microalgal flour, the biomass may be agitated or passed through a screen. The microalgal flour may also be mixed with other ingredients to make a soup, sauce, dough, cake, cookie, dry baked-good mix, etc. Testing can also be performed according to Examples 4, 5 and 8, below.

In accordance with embodiments of the invention, any two or more of the above-mentioned techniques can be combined to reach a heretofore unprecedented flavor in a microalgal biomass product, such as microalgal flour. For example, HTST treatment followed by washing with liquid as described above can produce microalgal flour having low off-flavor. Oxygenation during cultivation and other steps as described above may further improve the flavor.

By selecting an appropriate microalgal strain and using the methods disclosed herein, a microalgal biomass or flour made from the biomass having acceptable sensory characteristics may result. The microalgal flour may be non-green and have undetectable levels of fish, mushroom or cabbage flavors or odors when diluted in water at a ratio (by volume) of 1:2, 1:5, 1:10, 1:20, 1:30, or 1:40. In an embodiment, off flavors of fish and cabbage are undetectable when diluted 1:20 by volume in water, as detected by a tasting panel.

The following flavor/odor compounds were determined by the methods of Examples 4 or 5 and are believed to correlate with acceptable sensory testing: undecalactone (400-1800 ppb), 3-methyl butanal (0-11,000 ppb), pentanal (160-10,700 ppb), 2-methyl butanal (0-2500 ppb), 2-pentanone (39-10,600 ppb), 3-pentene-2-one (0-1500 ppb).

Acceptable samples also had less than threshold amounts of pyrrole, pyrazine, or pyridines-containing compounds, while these compounds were found in the sample of Chlorella vulgaris obtained from www.nuts.com, which was green and unacceptable in flavor and odor.

In an embodiment, the microalgal flour produced by the methods described above retain the low amounts of off-flavors mentioned for at least 2 weeks, 1 month, 3 months or 6 months when stored in the dark at room temperature in moisture and oxygen impermeable packaging (e.g. a Mylar® food storage bag).

Optionally, larger particles, granules or pellets can be made from the dried microalgal material. For example, the flour can be agglomerated, granulated, extruded, or pelletized using a variety of methods known in the art.

Example 1. Production of Microalgal Flour at Low pH and Using a Low-Pigment Strain

Multiple fermentations of Chlorella protothecoides were performed at scales ranging from 7 L to 1000 L. Two strains of Chlorella protothecoides were used: strain A, and strain B, a low-pigment mutant. Fermentation was performed in the dark on glucose as a fixed carbon source at a pH of about 5 to 6. After fermentation, the fermentation broth containing the microalgae was heat treated to inactivate the microalgae, immediately diluted with excess water, centrifuged to wash and concentrate the microalgae, the cells were lysed by milling, then spray-dried to make a microalgal flour. The microalgal flour made from Strain A was light yellow in color and the microalgal flour made from strain B was tan in color. A fermentation of strain B was also performed at about neutral pH.

Example 2. Low-Color Flour Using High Oxygen Conditions

Strain B was cultivated in at high (about 60%-70%) and low levels (about 30-40%) of dissolved oxygen and treated as in Example 1 to form microalgal flour. For the high oxygen experiment, reduced yellow color was noted in the broth, centrifuged biomass and in the final flour as compared to the microalgae produced at lower oxygen.

Example 3. Production of Improved Microalgal Flour

A seed culture of Chlorella protothecoides was added to a defined medium broth to give 9,000 L of culture. Heat-sterilized glucose (55% w/w) was used as a carbon source. Dissolved oxygen was held to a minimum of 30% by controlling aeration, backpressure and agitation in the fermentor. The cultivation temperature was 28° C. The pH of the broth was 6.8 at the start of cultivation and dropped to about 6 over the course of cultivation. Glucose was fed to a concentration of 3-10 g/L concentration. Growth was continued over 4-5 days to the mid-log-phase as measured by OD750. The resulting product had a dry cell weight (DCW) of 18.5% w/v. The nitrogen level in the growth medium was limiting to force the microalgae to accumulate approximately 50% lipid as a result of extended sugar feeding.

The broth was then heat-treated by online HTST at 75° C. for 1 min and cooled to 6.2° C., then stored at 7° C. The HTST-treated broth was then washed by 6.4-fold dilution in decarbonated water and centrifuged using an Alfa Laval FEUX 510 centrifuge.

The pH was lowered to pH to 4.1 with 75% phosphoric acid and 500 ppm sodium benzoate/1000 ppm potassium sorbate (on dry basis) were added as a preservative.

The material was then stored under agitation below 10° C.

Lysis was accomplished by milling in a NETZSCH LME500 bead mill using 0.5 mm zirconium silicate beads to give 88% cell disruption. The outlet was cooled to 6° C.

Ascorbic acid (150 ppm on a dry basis) and mixed tocopherols (500 ppm on a dry basis) were added to the material to prevent oxidation. Potassium hydroxide was added to neutralize the pH.

The material was then heated to 77° C. for 3 minutes.

Drying was accomplished on a Filtermat FMD125 drier with a cyclone. The nozzle pressure was 160-170 bar.

Example 4. SPME (SolidPhase MicroExtraction)

Samples (500 mg) plus 3 mL distilled water plus 1 gm NaCl plus 5 uL 0.022 ug/uL 2-undecanone in ethanol internal standard were incubated at 50° C. for 10 min and then extracted by SPME at 50° C. for 20 min while stirring with the orbital shaker of the Gerstel MPS2. The SPME fiber used was DVB/CAR/PDMS (Divinylbenzene/Carboxen/Polydimethylsiloxane), df 50/30 μm. The fiber was desorbed at 260° C. in the Agilent split/splitless injector for 3 min. Volatiles were desorbed into a Leco Pegasus GC-TOFMS and separated on a DB5-MS column (30 m, 0.25 mm, 0.25 um) with helium carrier gas flow at 1.0 mL/min. The initial column temperature was 40° C. (for 3 min) and then increased to 270° C. at 15° C./min and held at 270° C. for 5 min. Mass detection was performed in the electron impact mode (EI). All injections were splitless. Peak identification is based on comparison of EI mass spectra in samples to EI mass spectra of the NIST Library. Data is reported as relative concentration compared to the internal standard expressed in ppb

Example 5. SBSE (StirBar Sorptive Extraction)

Samples (500 mg) plus 10 mL distilled water plus 5 uL 0.022 ug/uL 2-undecanone internal standard in ethanol were extracted for 1 hr while stirring at 1000 rpm using a 2 cm Gerstel PDMS Twister. One gram of NaCl was then added to the sample and extraction was continued for another hour. The technique is known as sequential SBSE. The Twister is then removed from the sample, rinsed with distilled water, patted dry with a lintless cloth and thermally desorbed in a Gerstel TDU used in the splitless mode. With the TDU, desorbed volatiles were initially trapped at −100° C.; the volatiles trapped on the Twister were then desorbed at 280° C. for 3 min. Volatiles were desorbed into an Agilent GC-MSD and separated on a DB5-MS column (30 m, 0.25 mm, 0.25 um) with helium carrier gas flow at 1.0 mL/min. The initial column temperature was 40° C. (for 3 min) and then increased to 270° C. at 10° C./min and held at 270° C. for 5 min. Mass detection was performed in the electron impact mode (EI). All injections were splitless. Peak identification is based on comparison of EI mass spectra in samples to EI mass spectra of the NIST Library. Data is reported as relative concentration compared to the internal standard expressed in ppb.

Example 6. Flavor/Odor Data for Acceptable Sample of Example 3

The sample produced in Example 3 was tested by sensory panel and analyzed by SPME and SBSE as in Examples 4 and 5. The results are reported in the table below in units of parts per billion, determined relative to the 2-undecanone internal standard. In the tables below, a is used to represent alpha, d for delta, g for gamma. CAS numbers for the compounds are listed in Example 7.

Mean relative Chemical concentration Dimethyl.sulfide 0 2.3.Butanedione 248 Butanal 9.5 Propanal..2.methyl. 75 Furan..3.methyl. 67.5 Ethyl.Acetate 1671.5 2.Butenal...E.. 47.5 Butanal..3.methyl. 0 1.Butanol 26 Butanal..2.methyl. 0 Thiophene 0 1.Penten.3.ol 0 1.Penten.3.one 7 2.Pentanone 38.5 2.3.Pentanedione 688.5 Pentanal 2876 Furan..2.ethyl. 2 Thiazole 0 3.Penten.2.one 7.5 Disulfide..dimethyl 42 2.Pentenal...E.. 89.5 Pyrrole 0 Oxazole..4.5.dimethyl. 0 2.Penten.1.ol...Z.. 0 Thiophene..3.methyl. 68.5 Hexanal 16198 4.Methylthiazole 0 Pyrazine..methyl. 0 Furfural 0 Oxazole..trimethyl. 0 Butanoic.acid..3.methyl. 0 Butanoic.acid..2.methyl. 0 2.Hexenal 0 1.Hexanol 0 4.Heptanone 415 Pyridine..2.6.dimethyl. 0 Thiazole..2.4.dimethyl. 0 3.Heptanone 174 2.Heptanone 104 3.Heptanol 2426.5 Heptanal 700.5 Methional 0 Pyrazine..2.5.dimethyl. 0 Pyrazine..2.6.dimethyl. 0 Pyrazine..ethyl. 0 Pyrazine..2.3.dimethyl. 0 Pyrazine..ethenyl. 0 Thiazole..4.5.dimethyl. 0 2.Heptanone..6.methyl. 0 Hexanal..2.ethyl. 75 2.Heptenal...Z.. 493 5.Nonen.2.one 0 2.Furancarboxaldehyde..5.methyl...cooked.milk. 0 Benzaldehyde 231 hexanoic.acid 38.5 1.Octen.3.ol 173 Dimethyl.trisulfide 0 2.5.Octanedione 87.5 5.Hepten.2.one..6.methyl. 107.5 Furan..2.pentyl. 1.5 2.4.Heptadienal...E.E.. 0 Pyrazine..2.ethyl.6.methyl. 0 Octanal 1067 Pyrazine..trimethyl. 0 Pyrazine..2.ethyl.3.methyl. 0 2.4.Heptadienal...E.E...1 13.5 Pyrazine..2.ethenyl.6.methyl. 0 1.Hexanol..2.ethyl. 11445.5 3.Octen.2.one...E.. 0 2H.Pyran.2.one..5.6.dihydro. 1472 Benzeneacetaldehyde 0 3.5.Octadien.2.one...E.E.. 0 Acetophenone 74 1.Decen.3.one 0 Pyrazine..3.ethyl.2.5.dimethyl. 0 Pyrazine..tetramethyl. 0 5.Methyl.2.thiophenecarboxaldehyde 0 g.Heptalactone 0 Linalool 0 Nonanal 1436.5 Thymol 0 Phenylethyl.Alcohol 0 2.3.5.Trimethyl.6.ethylpyrazine. 0 Acetic.acid..phenylmethyl.ester 179.5 Safranal 0 2.Decenal...E.. 150 g.octalacone 0 o.Amino.acetophenone 0 2.4.Decadienal 0 g.Nonlactone 0 Ionone 0 Geranyl.acetone 0 Ionene 0 g.Nonlactone.1 0 2.4.Nonadienal...E.E.. 0 2.4.Decadienal.1 17.980041 g.Heptalactone.1 0 Ionone.1 0 Geranyl.acetone.1 0 a.Ionone 0 Peach.lactone.g.undecalactone 46.4516735 d.Decalactone 186.835836 cis.Geranylacetone 0 d.dodecalactone..δ.Nonyl.δ.valeralactone. 1582.590707 d.Undecalactone 11295.4731

Example 7. PCA Analysis

Multiple production lots of Chlorella protothecoides microalgal flour were produced according to methods given above. In addition, a commercial sample of Chlorella powder was obtained from nuts.com; the product information as of the date of filing. http://www.nuts.com/ assigns the flour to a Korean source, with heterotrophic production. A total of 12 samples, measured in duplicate by SBSE and SPME as in Examples 4 and 5, were used. In addition, sensory testing was done using a panel of volunteers. Scaled principal component analysis (using a correlation matrix) was performed with R software version 2.15.1 (The R project for Statistical Computing, www.r-project.org) using the prcomp function. Three principal components were found that well characterize the variation in flavor/odor compounds. Vectors defining the three principal components are listed in the table below as PC1, PC2, and PC3 along with the method used for determining each compound. A cluster of samples was found in this reduced-dimensional space that correlated with the samples having acceptable sensory characteristics.

GC Chemical Name CAS PC1 PC2 PC3 Method Dimethyl sulfide 75-18-3 0.0076 −0.154649 0.1379564 SPME 2,3-Butanedione 431-03-8 −0.05341 0.116238 0.1384577 SPME Butanal 123-72-8 −0.0612 0.021748 −0.1541993 SPME Propanal, 2-methyl- 78-84-2 −0.0248 −0.203551 0.1420793 SPME Furan, 3-methyl- 930-27-8 −0.13905 0.053489 −0.0400092 SPME Ethyl Acetate 141-78-6 0.02303 0.078633 0.1490604 SPME 2-Butenal, (E)- 123-73-9 0.0346 −0.007869 −0.2288552 SPME Butanal, 3-methyl- 590-86-3 −0.01585 −0.209996 0.152554 SPME 1-Butanol 71-36-3 0.01482 0.147081 0.1203239 SPME Butanal, 2-methyl- 96-17-3 −0.06977 −0.186611 0.1433748 SPME Thiophene 110-02-1 −0.14535 0.003674 −0.0107213 SPME 1-Penten-3-ol 616-25-1 −0.10591 0.05907 −0.0208901 SPME 1-Penten-3-one 1629-58-9 0.02932 −0.055926 −0.1865801 SPME 2-Pentanone 107-87-9 0.01895 −0.168215 0.1843823 SPME 2,3-Pentanedione 600-14-6 0.03772 −0.074626 −0.0103901 SPME Pentanal 110-62-3 −0.05954 −0.059048 −0.1301291 SPME Furan, 2-ethyl- 3208-16-0 −0.00841 −0.0761 −0.0141672 SPME Thiazole 288-47-1 −0.14288 −0.031332 0.0205445 SPME 3-Penten-2-one 625-33-2 0.03658 −0.118624 0.1932202 SPME Disulfide, dimethyl 624-92-0 0.00766 0.07675 −0.030508 SPME 2-Pentenal, (E)- 1576-87-0 0.02904 0.005659 −0.0633539 SPME Pyrrole 109-97-7 −0.14542 0.001009 −0.0083546 SPME Oxazole, 4,5-dimethyl- 20662-83-3 −0.14535 0.003674 −0.0107213 SPME 2-Penten-1-ol, (Z)- 1576-95-0 −0.14181 −0.022408 −0.0072056 SPME Thiophene, 3-methyl- 616-44-4 0.00669 0.144512 0.1163417 SPME Hexanal 66-25-1 0.02329 0.064197 −0.1621187 SPME 4-Methylthiazole 693-95-8 −0.14535 0.003674 −0.0107213 SPME Pyrazine, methyl- 109-08-0 −0.13884 −0.055436 0.0337262 SPME Furfural 98-01-1 −0.14535 0.003674 −0.0107213 SPME Oxazole, trimethyl- 20662-84-4 −0.14535 0.003674 −0.0107213 SPME Butanoic acid, 3-methyl- 503-74-2 −0.14535 0.003674 −0.0107213 SPME Butanoic acid, 2-methyl- 116-53-0 −0.14535 0.003674 −0.0107213 SPME 2-Hexenal 505-57-7 0.02747 −0.052249 −0.2361552 SPME 1-Hexanol 111-27-3 0.03121 0.198559 0.0119837 SPME 4-Heptanone 123-19-3 −0.00358 −0.135096 0.0100197 SPME Pyridine, 2,6-dimethyl- 108-48-5 −0.14535 0.003674 −0.0107213 SPME Thiazole, 2,4-dimethyl- 541-58-2 −0.14535 0.003674 −0.0107213 SPME 3-Heptanone 106-35-4 0.02161 −0.184446 −0.1716557 SPME 2-Heptanone 110-43-0 −0.09702 −0.058868 0.0154171 SPME 3-Heptanol 589-82-2 0.02303 −0.205456 −0.1113283 SPME Heptanal 111-71-7 −0.11331 0.141566 −0.0259176 SPME Methional 3268-49-3 −0.11001 −0.130401 0.0939776 SPME Pyrazine, 2,5-dimethyl- 123-32-0 0.02063 −0.11695 −0.0042558 SPME Pyrazine, 2,6-dimethyl- 108-50-9 −0.14539 −0.007146 −0.0010984 SPME Pyrazine, ethyl- 13925-00-3 −0.14544 −4.79E−05 −0.0074156 SPME Pyrazine, 2,3-dimethyl- 5910-89-4 −0.14541 0.001518 −0.0088075 SPME Pyrazine, ethenyl- 4177-16-6 −0.14535 0.003674 −0.0107213 SPME Thiazole, 4,5-dimethyl- 3581-91-7 −0.14535 0.003674 −0.0107213 SPME 2-Heptanone, 6-methyl- 928-68-7 −0.14535 0.003674 −0.0107213 SPME Hexanal, 2-ethyl- 123-05-7 0.01846 −0.027007 −0.1799374 SPME 2-Heptenal, (Z)- 57266-86-1 0.02161 −0.093801 −0.1905916 SPME 5-Nonen-2-one 27039-84-5 −0.14535 0.003674 −0.0107213 SPME 2-Furancarboxaldehyde, 5-methyl- 620-02-0 0.01921 −0.109621 0.1754483 SPME Benzaldehyde 100-52-7 −0.14243 0.046336 0.0247769 SPME hexanoic acid 109-52-4 −0.00113 0.064879 −0.0160903 SPME 1-Octen-3-ol 3391-86-4 −0.09067 −0.045064 −0.1354748 SPME Dimethyl trisulfide 3658-80-8 0.0289 −0.064852 −0.1508671 SPME 2,5-Octanedione 3214-41-3 0.02899 −0.075905 −0.0937522 SPME 5-Hepten-2-one, 6-methyl- 110-93-0 −0.14527 0.00547 −0.0141759 SPME Furan, 2-pentyl- 3777-69-3 −0.07838 0.16758 −0.0356101 SPME 2,4-Heptadienal, (E,E)- 4313-03-5 0.024 −0.071588 −0.1450388 SPME Pyrazine, 2-ethyl-6-methyl- 13925-03-6 −0.14535 0.003674 −0.0107213 SPME Octanal 124-13-0 0.06342 0.197764 −0.0144755 SPME Pyrazine, trimethyl- 14667-55-1 −0.14463 −0.018889 0.0093576 SPME Pyrazine, 2-ethyl-3-methyl- 15707-23-0 −0.14535 0.003674 −0.0107213 SPME 2,4-Heptadienal, (E,E)- 4313-03-5 0.03375 −0.100784 −0.1998281 SPME Pyrazine, 2-ethenyl-6-methyl- 13925-09-2 −0.14535 0.003674 −0.0107213 SPME 1-Hexanol, 2-ethyl- 104-76-7 0.01545 −0.147033 −0.1738968 SPME 3-Octen-2-one, (E)- 18402-82-9 0.02243 −0.027669 −0.1418 SPME 2H-Pyran-2-one, 5,6-dihydro- 3393-45-1 0.04024 0.008083 −0.0019753 SPME Benzeneacetaldehyde 122-78-1 0.01141 −0.200551 0.1476711 SPME 3,5-Octadien-2-one, (E,E)- 30086-02-3 0.02431 0.191552 −0.0405352 SPME Acetophenone 98-86-2 0.03482 0.112029 0.0678319 SPME 1-Decen-3-one 56606-79-2 0.01487 −0.007144 0.0679731 SPME Pyrazine, 3-ethyl-2,5-dimethyl- 13360-65-1 −0.14539 0.002524 −0.0097007 SPME Pyrazine, tetramethyl- 1124-11-4 −0.14544 −0.003912 −0.0054264 SPME 5-Methyl-2- 13679-70-4 −0.14535 0.003674 −0.0107213 SPME thiophenecarboxaldehyde g-Heptalactone 105-21-5 0.01298 0.140814 0.1183756 SPME Linalool 78-70-6 −0.14535 0.003674 −0.0107213 SPME Nonanal 124-19-6 0.05356 0.198786 −0.1092893 SPME Thymol 89-83-8 −0.14535 0.003674 −0.0107213 SPME Phenylethyl Alcohol 60-12-8 −0.14506 −0.014282 0.003239 SPME 2,3,5-Trimethyl-6-ethylpyrazine 17398-16-2 −0.14538 0.002837 −0.0099785 SPME Acetic acid, phenylmethyl ester 140-11-4 0.04544 0.114759 0.1539536 SPME Safranal 116-26-7 −0.14535 0.003674 −0.0107213 SPME 2-Decenal, (E)- 3913-81-3 0.03435 −0.01297 −0.2149363 SPME g-Octalactone 104-50-7 0.01639 0.142953 0.0964521 SPME o-Amino acetophenone 551-93-9 0.02232 0.204042 0.0183701 SPME 2,4-Decadienal 2363-88-4 0.01791 0.169004 −0.0389474 SBSE g-Nonlactone 104-61-0 0.01493 0.18923 0.0333768 SPME a-Ionone 127-41-3 −0.14535 0.003674 −0.0107213 SPME Geranyl acetone 3796-70-1 −0.14542 −0.002004 −0.0085515 SPME a-Ionene 14901-07-6 −0.14535 0.003674 −0.0107213 SBSE g-Nonalactone 104-61-0 0.01637 −0.075372 −0.0496326 SBSE 2,4-Nonadienal 6750-03-4 0.03136 −0.023742 −0.1745061 SBSE 2,4-Decadienal 2363-88-4 0.02952 0.094377 −0.1710607 SBSE g-Heptalactone 105-21-5 0.01775 0.158721 −0.0198467 SBSE a-Ionone 127-41-3 −0.14535 0.003674 −0.0107213 SBSE Geranyl acetone 3796-70-1 −0.14535 0.003674 −0.0107213 SBSE a-Ionone 127-41-3 −0.14535 0.003674 −0.0107213 SBSE g-Undecalactone 104-67-6 0.09703 −0.071462 0.0844344 SBSE d-Decalactone 705-86-2 0.03467 −0.188054 0.0770618 SBSE cis-Geranylacetone 3879-26-3 0.01193 0.016184 −0.0633938 SBSE d-Dodecalactone.. 713-95-1 0.13073 −0.059213 0.0333184 SBSE d-Undecalactone 710-04-3 0.05183 −0.042457 −0.1311766 SBSE

The graph provided in FIG. 2 shows the PCA analysis clustering. Each plotted point represents a microalgal powder sample plotted in a space defined by the principal components PC1, PC2, and PC3 (dim1, dim2 and dim3 respectively). The solid circles represent Chlorella protothecoides flour samples that has acceptable flavor. The open circles represent Chlorella protothecoides flour samples with inferior flavor. The open square represent the Chlorella vulgaris obtained from Nuts.com.

Example 8. Determination of Bounds for Acceptable Flavor

Based on the PCA analysis of Example 7, the FactomineR package v. 1.2.1 (Husson, et al.) was used to statistically define the cluster of samples that correlated with the acceptable sensory testing. The result of the FactomineR analysis was 3 ellipsoids in the three dimensions of PC1, PC2 and PC3; the ellipsoids characterize 1, 2, and 3 standard deviations from center point of the cluster associated with the positive human sensory analysis (solid circles from the graph shown in FIG. 2). Each 3-dimensional ellipsoid is defined by 3 orthogonal 2-dimensional ellipses defined by the equation Ax²+Bxy+Cy²+Dx+Ey+F=0 using the data in the table below for the values of A, B, C, D, E, and F. Thus, samples falling within the smallest ellipsoid will be expected to have a positive sensory analysis by a human panel about 99.7% of the time, samples falling within only the mid-sized ellipsoid will be expected to have a positive sensory analysis by a human panel about 95% of the time, and samples falling only within the largest ellipsoid will be expected to have a positive sensory analysis by a human panel about 68% of the time.

Equation for Confidence Intervals: Ax ² +Bxy+Cy ² +Dx+Ey+F=0  Equation

Standard X Y Deviations Dimension Dimension A B C D E F 3 PC1 PC2 0.003481467 −0.000366174  3.79437E−05 −0.000628924 4.27301E−05 1.51548E−05 3 PC1 PC3 0.001734328 0.000286969 1.89401E−05 −0.000318201 −2.8099E−05 1.12003E−05 3 PC2 PC3 0.356218856 0.289219807 0.356936631 0.085191149 −0.040237159 −0.13812915  2 PC1 PC2 0.000477458 −5.02181E−05   5.2037E−06 −8.62524E−05 5.86012E−06 3.01302E−06 2 PC1 PC3 0.00023785 3.93556E−05  2.5975E−06  −4.3639E−05 −3.85357E−06  1.76892E−06 2 PC2 PC3 0.048852827 0.039664394 0.048951264 0.011683347 −0.005518234 −0.009118978 1 PC 1 PC 2 2.78319E−05 −2.9273E−06 3.03333E−07  −5.0278E−06 3.41597E−07 2.11154E−07 1 PC 1 PC 3 1.38647E−05 2.29411E−06 1.51413E−07 −2.54379E−06 −2.24631E−07  1.11963E−07 1 PC 2 PC 3 −0.000665829 0.000466136 −0.000152694  0.000380618 −0.000136456 −4.14371E−05 

Example 9. QC Analysis Using Results of PCA Analysis

The ellipsoids of Example 8 can be used to determine if a sample falls within the cluster associated with positive flavor. For example, a quality-control experiment can be performed on a batch of microalgal flour produced according to the methods given above. The flour is analyzed by SPME and SBSE as in Examples 4 and 5 and then one determines if the data falls within one or more of the ellipsoids of Example 8.

To do this, one can use the following procedure (though others may be applicable): Start with relative concentration for 105 compounds. From each concentration subtract it's center factor and divide by its scale factor (given in the table below), this centers and scales the data. Take the dot product of the scaled and centered data and the principal component (PC) loadings, this will yield one value for each PC. Divide each value by its associated plotting factor, this will allow the data point to be plotted in three dimensional algal-chemical space. If the point falls within the space bounded by the confidence ellipsoid it is not statistically different (p<0.05). For example, if the point falls within the space bounded by the 95% confidence ellipsoid it is not statistically different (p<0.05).

Chemical Center Scale PC1 PC2 PC3 Dimethyl.sulfide 15.04166667 52.10586179 0.007602386 −0.154648539 0.13795639 2.3.Butanedione 573.4583333 687.3035077 −0.053406645 0.116238372 0.138457708 Butanal 165.0833333 291.8766733 −0.061200873 0.021748265 −0.154199309 Propanal..2.methyl. 294.25 321.9922006 −0.02479716 −0.203551061 0.142079295 Furan..3.methyl. 254.0833333 364.0905752 −0.139050167 0.053488926 −0.040009249 Ethyl.Acetate 1534.958333 721.2414001 0.023033335 0.078632968 0.149060426 2.Butenal...E.. 56.95833333 67.74264748 0.034598984 −0.007869304 −0.228855217 Butanal..3.methyl. 2368.958333 3305.894731 −0.015854973 −0.209996041 0.152553963 1.Butanol 236.75 723.0508438 0.01482126 0.147080874 0.120323863 Butanal..2.methyl. 858.0416667 1132.843254 −0.069765232 −0.186610612 0.143374765 Thiophene 0.708333333 2.453738644 −0.145349572 0.003673658 −0.010721336 1.Penten.3.ol 111.2916667 123.2715883 −0.105910877 0.059069801 −0.020890092 1.Penten.3.one 10.625 18.86570361 0.029319785 −0.055925743 −0.186580083 2.Pentanone 429.875 520.4705967 0.018948769 −0.168215403 0.184382338 2.3.Pentanedione 392.625 359.8726495 0.037715762 −0.074625863 −0.010390137 Pentanal 5315.166667 4258.727501 −0.05954475 −0.05904769 −0.130129097 Furan..2.ethyl. 32.75 24.43590875 −0.008414663 −0.076099651 −0.014167153 Thiazole 70.16666667 199.0549642 −0.142882049 −0.031332244 0.020544457 3.Penten.2.one 442.125 470.5612763 0.036579138 −0.118623927 0.193220234 Disulfide..dimethyl 77.45833333 105.2821875 0.007660621 0.076749927 −0.030508003 2.Pentenal...E.. 116.7083333 200.60312 0.029036734 0.005658787 −0.063353931 Pyrrole 12.29166667 41.79846579 −0.145424967 0.001008736 −0.008354639 Oxazole..4.5.dimethyl. 15.83333333 54.84827557 −0.145349572 0.003673658 −0.010721336 2.Penten.1.ol...Z.. 45.25 118.0232065 −0.141807908 −0.022407562 −0.007205637 Thiophene..3.methyl. 108.5416667 279.7959856 0.006693629 0.144512146 0.116341706 Hexanal 26189.95833 17886.61913 0.023290612 0.064196972 −0.162118696 4.Methylthiazole 1.958333333 6.783865663 −0.145349572 0.003673658 −0.010721336 Pyrazine..methyl. 135.2083333 326.6405766 −0.138842567 −0.055435505 0.03372617 Furfural 34.5 119.5115057 −0.145349572 0.003673658 −0.010721336 Oxazole..trimethyl. 64 221.7025034 −0.145349572 0.003673658 −0.010721336 Butanoic.acid..3.methyl. 58.58333333 202.9386196 −0.145349572 0.003673658 −0.010721336 Butanoic.acid..2.methyl. 3.833333333 13.27905619 −0.145349572 0.003673658 −0.010721336 2.Hexenal 25.58333333 50.09710268 0.027469429 −0.052249399 −0.23615517 1.Hexanol 106.1666667 155.9474465 0.031207096 0.198558566 0.011983686 4.Heptanone 360.5833333 577.8576749 −0.003575779 −0.135096305 0.010019679 Pyridine..2.6.dimethyl. 2.958333333 10.24796728 −0.145349572 0.003673658 −0.010721336 Thiazole..2.4.dimethyl. 15.58333333 53.98225017 −0.145349572 0.003673658 −0.010721336 3.Heptanone 111.625 94.41016052 0.021607662 −0.18444557 −0.171655667 2.Heptanone 380.875 288.460973 −0.097016748 −0.058868123 0.015417076 3.Heptanol 1193.041667 1008.348074 0.023029974 −0.205456135 −0.111328282 Heptanal 1396.791667 920.0702903 −0.113307135 0.141565621 −0.025917554 Methional 79.625 148.3023823 −0.110012922 −0.130400953 0.093977633 Pyrazine..2.5.dimethyl. 3.333333333 7.857634774 0.020631611 −0.116950274 −0.004255769 Pyrazine..2.6.dimethyl. 178.2083333 574.8013672 −0.145388496 −0.007146465 −0.001098366 Pyrazine..ethyl. 15.95833333 53.8796885 −0.145442956 −0.0000479 −0.007415618 Pyrazine..2.3.dimethyl. 439.2083333 1498.775644 −0.145413873 0.001518449 −0.008807482 Pyrazine..ethenyl. 1.416666667 4.907477288 −0.145349572 0.003673658 −0.010721336 Thiazole..4.5.dimethyl. 3.583333333 12.41303079 −0.145349572 0.003673658 −0.010721336 2.Heptanone..6.methyl. 53.75 186.1954618 −0.145349572 0.003673658 −0.010721336 Hexanal..2.ethyl. 78.41666667 124.9672381 0.018460956 −0.027007294 −0.179937424 2.Heptenal...Z.. 645.25 937.3877266 0.021607084 −0.093800543 −0.190591625 5.Nonen.2.one 13.33333333 46.18802154 −0.145349572 0.003673658 −0.010721336 2.Furancarboxaldehyde..5.methyl...cooked.milk. 21.25 40.57288615 0.019206035 −0.109620677 0.175448337 Benzaldehyde 872.875 1358.161493 −0.142431906 0.046335544 0.024776943 hexanoic.acid 176.25 216.4210438 −0.001128927 0.064879481 −0.016090326 1.Octen.3.ol 369.6666667 350.9919277 −0.090672545 −0.045064295 −0.135474824 Dimethyl.trisulfide 14.33333333 21.56315601 0.028899179 −0.064852089 −0.150867075 2.5.Octanedione 23.95833333 44.27674248 0.028988465 −0.07590479 −0.093752193 5.Hepten.2.one..6.methyl. 1503.833333 4827.634134 −0.145266246 0.005470194 −0.014175912 Furan..2.pentyl. 633 967.4016276 −0.078384616 0.167579691 −0.035610073 2.4.Heptadienal...E.E.. 20.83333333 43.16371231 0.024003523 −0.071588186 −0.145038829 Pyrazine..2.ethyl.6.methyl. 21 72.74613392 −0.145349572 0.003673658 −0.010721336 Octanal 1243.041667 897.5365644 0.063418428 0.197764097 −0.01447548 Pyrazine..trimethyl. 348.6666667 1051.439497 −0.144625394 −0.018888681 0.009357594 Pyrazine..2.ethyl.3.methyl. 87.33333333 302.5315411 −0.145349572 0.003673658 −0.010721336 2.4.Heptadienal...E.E...1 26.33333333 40.42070427 0.033749609 −0.100784032 −0.199828071 Pyrazine..2.ethenyl.6.methyl. 5.541666667 19.19689645 −0.145349572 0.003673658 −0.010721336 1.Hexanol..2.ethyl. 5684.541667 5078.453328 0.015454406 −0.147033095 −0.173896762 3.Octen.2.one...E.. 196.375 462.4334412 0.022433793 −0.027668713 −0.141800019 X2H.Pyran.2.one..5.6.dihydro. 683.3333333 845.025291 0.040235145 0.008083104 −0.001975331 Benzeneacetaldehyde 31.83333333 60.74811383 0.01141478 −0.200551415 0.147671091 3.5.Octadien.2.one...E.E.. 455.125 426.6112306 0.024307307 0.191552198 −0.040535191 Acetophenone 42.375 56.41088104 0.034819826 0.112028714 0.067831917 1.Decen.3.one 3.125 9.100761706 0.014871492 −0.007143686 0.067973089 Pyrazine..3.ethyl.2.5.dimethyl. 50.75 174.3908228 −0.145387371 0.002524067 −0.009700663 Pyrazine..tetramethyl. 951.4583333 3113.918129 −0.145437121 −0.00391206 −0.005426362 5.Methyl.2.thiophenecarboxaldehyde 57.375 198.7528302 −0.145349572 0.003673658 −0.010721336 g.Heptalactone 2 6.92820323 0.012980337 0.140814237 0.118375646 Linalool 9.833333333 34.06366588 −0.145349572 0.003673658 −0.010721336 Nonanal 1528.416667 1335.036088 0.053558189 0.198785653 −0.109289305 Thymol 160.5833333 556.2769844 −0.145349572 0.003673658 −0.010721336 Phenylethyl.Alcohol 135.9583333 416.085189 −0.145061726 −0.01428243 0.003239013 2.3.5.Trimethyl.6.ethylpyrazine. 208.7083333 718.7459552 −0.145377878 0.002836895 −0.00997845 Acetic.acid..phenylmethyl.ester 213.875 205.6043337 0.045438482 0.114758954 0.153953593 Safranal 47.29166667 163.8231389 −0.145349572 0.003673658 −0.010721336 2.Decenal...E.. 55.04166667 78.60616976 0.034351801 −0.012969523 −0.21493625 g.octalacone 10.625 28.57933535 0.016392036 0.14295305 0.096452129 o.Amino.acetophenone 15.5 32.17070943 0.022315438 0.204041622 0.018370134 2.4.Decadienal 9.416666667 24.16781606 0.0179089 0.169004115 −0.038947428 g.Nonlactone 13.5 40.20345982 0.01493418 0.189230257 0.033376822 Ionone 101.3333333 351.0289637 −0.145349572 0.003673658 −0.010721336 Geranyl.acetone 652.75 2137.396627 −0.145423518 −0.002004031 −0.008551463 Ionene 159.7916667 553.5345706 −0.145349572 0.003673658 −0.010721336 g.Nonlactone.1 6.58755 22.81994259 0.016371012 −0.075372449 −0.049632645 2.4.Nonadienal...E.E.. 18.07305674 30.64101284 0.031363408 −0.023742328 −0.174506137 2.4.Decadienal.1 50.4716275 85.11825112 0.029518821 0.094376773 −0.171060695 g.Heptalactone.1 17.25928968 42.07909242 0.017750131 0.158720982 −0.019846703 Ionone.1 199.0162875 689.4126429 −0.145349572 0.003673658 −0.010721336 Geranyl.acetone.1 880.2922516 3049.421811 −0.145349572 0.003673658 −0.010721336 a.Ionone 335.0475951 1160.638915 −0.145349572 0.003673658 −0.010721336 Peach.lactone.g.undecalactone 72.77877498 34.06000193 0.097029409 −0.071461906 0.084434422 d.Decalactone 85.57314465 106.5309321 0.034674859 −0.18805394 0.077061807 cis.Geranylacetone 5.9584 20.64050306 0.011926134 0.016184168 −0.063393798 d.dodecalactone..δ.Nonyl.δ.valeralactone. 1400.955104 491.4817796 0.130734715 −0.059212775 0.033318423 d.Undecalactone 6472.792302 6394.323609 0.051826724 −0.042456918 −0.131176612 Plotting Factor: PC Standard Deviation * Square Root of number of samples from the model PC1 23.79781 PC2 12.25408 PCS 11.48665

Further Discussion of Embodiments of the Invention

In the following paragraphs, certain embodiments of the present invention have been numbered for convenience sake. The numbers associated with each embodiment are arbitrary and are not intended to indicate the relative importance of the various embodiments.

1. A microalgal flour suitable for use in food, the flour comprising microalgal cells of Chlorophyta, wherein analysis by SPME according to Example 4 and SBSE according to Example 5 to determine concentrations of the compounds of Example 6 relative to an internal standard, followed by analysis according to the procedure of Example 9 produces a flavor descriptor that falls within the ellipsoid of Example 8 defining 3 standard deviations relative to the positive flavor cluster corresponding to the closed circles in the graph of FIG. 2. 2. A microalgal flour of embodiment 1, wherein the flavor descriptor falls within the ellipsoid of Example 8 defining 2 standard deviations relative to the positive flavor cluster corresponding to the closed circles in the graph of FIG. 2. 3. A microalgal flour of any of the preceding embodiments, wherein the flavor descriptor falls within the ellipsoid of Example 8 defining 1 standard deviation relative to the positive flavor cluster corresponding to the closed circles in the graph of FIG. 2. 4. A microalgal flour of any of the preceding embodiments, obtainable by the process of:

-   -   cultivating a broth of cells of Chlorella protothecoides in the         dark in the presence of glucose as a fixed carbon source with a         starting pH of 6.8, while maintaining the dissolved oxygen level         above 30%, subjecting the broth to a high-temperature-short-time         process of 75° C. for 1 minute, harvesting the cells by         centrifugation with a dilution of 6.4 fold in water, adding an         antioxidant, lysis of the cells by milling, and drying using a         spray-dry nozzle outputting to a moving belt.         5. A microalgal flour of any of the preceding embodiments,         comprising undecalactone (400-1800 ppb), 3-methyl butanal         (0-11,000 ppb), pentanal (160-10,700 ppb), 2-methyl butanal         (0-2500 ppb), 2-pentanone (39-10,600 ppb), and/or         3-pentene-2-one (0-1500 ppb) as determined by SPME or SBSE.         6. A microalgal flour of any of the preceding embodiments,         having an undetectable fish or cabbage flavor when the flour is         dispersed in deionized water at 10% (w/v), as detected by a         tasting panel.         7. A microalgal flour of any of the preceding embodiments,         having a flowability characterized by an oversize of 15-35% by         weight at 2000 μm.         8. A microalgal flour according to any of the preceding         embodiments wherein the flour is white, pale yellow or yellow in         color.         9. A microalgal flour according to any of the preceding         embodiments, comprising no apparent green color.         10. A microalgal flour according to any of the preceding         embodiments, wherein the flour comprises 5-20% lipid.         11. A microalgal flour according to any of the preceding         embodiments, wherein the flour comprises 30-70% lipid.         12. A microalgal flour according to any of the preceding         embodiments, wherein the flour comprises 40-60% lipid.         13. A microalgal flour according to any of the preceding         embodiments, wherein the pH of the flour when dissolved in water         at 1% (w/v) is between 5.5 and 8.5.         14. A microalgal flour according to any of the preceding         embodiments, wherein the pH of the flour when dissolved in water         at 1% (w/v) is between 6.0 and 8.0.         15. A microalgal flour according to any of the preceding         embodiments, wherein the pH of the flour when dissolved in water         at 1% (w/v) is between 6.5 and 7.5.         16. A microalgal flour according to any of the preceding         embodiments, having less than 2 ppm of chlorophyll.         17. A microalgal flour according to any of the preceding         embodiments, further comprising an added antioxidant.         18. A microalgal flour according to any of the preceding         embodiments, wherein the majority of the cells in the flour are         lysed and optionally between 50 and 90% of the cells are lysed.         19. A microalgal flour obtainable by the process of:     -   cultivating a broth of cells of Chlorella protothecoides in the         dark in the presence of glucose as a fixed carbon source with a         starting pH of 6.8, while maintaining the dissolved oxygen level         above 30%, subjecting the broth to a high-temperature-short-time         process of 75° C. for 1 minute, harvesting the cells by         centrifugation with a dilution of 6.4 fold in water, lysis of         the cells by milling, adding an antioxidant, and drying using a         spray-dry nozzle outputting to a moving belt.

The described embodiments of the invention are intended to be merely exemplary and numerous variations and modifications will be apparent to those skilled in the art. All such variations and modifications are intended to be within the scope of the present invention as defined in the appended claims. 

What is claimed is:
 1. An edible microalgal flour suitable for use in food obtainable by the process of: cultivating Chlorella protothecoides cells heterotrophically in the dark in the presence of fixed carbon source while substantially maintaining the dissolved oxygen level above 30% until the microalgae reach a desired density and lipid concentration, subjecting the cells to a high-temperature-short-time pasteurization process; washing and harvesting the cells; lysing between 50% and 90% of the cells; and drying the lysed cells in a spray dryer; wherein the microalgal flour comprises a lipid content between 35% and 75% and less than 200 ppm of chlorophyll; and the microalgal flour comprises one or more compounds that define a flavor descriptor of the microalgal flour, said one or more compounds selected from the group consisting of: dimethyl sulfide, 2,3-butanedione, butanal, 2-methylpropanal, 3-methyl furan, ethyl acetate, (2E)-but-2-enal, 3-methyl-butanal, 1-butanol, 2-methyl butanal, thiophene, 1-pentene-3-ol, 1-penten-3-one, 2-pentanone, 2,3-pentanedione, pentanal, 2-ethyl furan, thiozole, 3-penten-2-one, dimethyl disulfide, E-2-pentenal, pyrrole, 4,5-dimethyl oxazole, cis-2-Penten-1-ol, 3-methyl thiophene, hexanal, 4-methyltyhiazole, methyl pyrazine, furfural, trimethyl oxaxole, 3-methyl butanoic acid, 2-methyl butanoic acid, 2-hexenal, 1-hexanol, 4-heptanone, 2,6-dimethyl pyridine, 2,4-dimethyl thiazole, 3-heptanone, 2-heptanone, 3-heptanol, heptanal, methional, 2,5-dimethyl pyrazine, 2,6-dimethyl pyrazine, ethyl pyrazine, 2,3-dimethyl pyrazine, ethenyl pyrazine, 4,5-dimethyl thiazole, 6-methyl-2-heptanone, 2-ethyl hexanal, (Z)-2-Heptenal, non-3-en-2-one, 5-methyl furfural, benzaldehyde, hexanoic acid, 1-octen-3-ol, dimethyl.trisulfide, 2,5-octanedione, 6-methyl-5-hepten-2-one, 2-pentyl furan, (2E,4E)-hepta-2,4-dienal, 2-ethyl-6-methylpyrazine, octanal, trimethyl pyrazine, 2-ethyl-3-methyl pyrazine, 2-ethylhexanol, E-3-octen-2-one, 5,6-dihydro-2H-pyran-2-one, benzeneacetaldehyde, 3,5-Octadiene-2-one, acetophenone, 1-octen-3-one, 2,5-dimethyl-3-ethylpyrazine, tetramethyl pyrazine, 5-methyl-2-thiophenecarboxaldehyde, g-heptalactone, linalool, nonanal, thymol, phenethyl alcohol, 2,3,5-trimethyl-6-ethyl pyrazine, benzyl acetate, safranal, E-2-decenal, g-octalacone, o-amino.acetophenone, 2,4-decadienal, g-nonalactone, ionone, geranyl acetone, ionene, 2,4-nonadienal, 2,4-decadienal, g-undecalactone, d-decalactone, cis-geranylacetone, δ-Dodecalactone, and d-undecalactone; and the flavor descriptor falls within a three-dimensional ellipsoid in a flavor-description space having dimensions defined by three principle components, PC1, PC2, and PC3, the ellipsoid defined by the equation: A _(x) ² +B _(xy) +C _(y) ² +D _(x) +E _(y) +F=0, wherein A, B, C, D, E, and F are defined below and represent three standard deviations from the center point of the ellipsoid: X Y A B C PC1 PC2 0.003481467 −0.000366174 3.79437E−05 PC1 PC3 0.001734328 0.000286969 1.89401E−05 PC2 PC3 0.356218856 0.289219807 0.356936631 X Y D E F PC1 PC2 −0.000628924   4.27301E−05 1.51548E−05 PC1 PC3 −0.000318201  −2.8099E−05 1.12003E−05 PC2 PC3 0.085191149 −0.040237159 −0.13812915

wherein the flavor descriptor represents a property of the microalgal flour.
 2. The edible microalgal flour of claim 1, wherein A, B, C, D, E, and F are defined below and represent two standard deviations from the center point of the ellipsoid: X Y A B C D E F PC1 PC2 0.000477458 −5.02181E−05 5.2037E−06 −8.62524E−05   5.86012E−06 3.01302E−06 PC1 PC3 0.00023785   3.93556E−05 2.5975E−06  −4.3639E−05 −3.85357E−06 1.76892E−06 PC2 PC3 0.048852827 0.039664394 0.048951264 0.011683347 −0.005518234 −0.009118978.


3. The edible microalgal flour of claim 1, wherein A, B, C, D, E, and F are defined below and represent one standard deviation from the center point of the ellipsoid: X Y A B C D E F PC1 PC2 2.78319E−05  −2.9273E−06 3.03333E−07  −5.0278E−06   3.41597E−07   2.11154E−07 PC1 PC3 1.38647E−05   2.29411E−06 1.51413E−07 −2.54379E−06 −2.24631E−07   1.11963E−07 PC2 PC3 −0.000665829 0.000466136 −0.000152694 0.000380618 −0.000136456 −4.14371E−05.


4. The edible microalgal flour of claim 1, wherein the fixed carbon source is glucose.
 5. The edible microalalgal flour of claim 1, wherein cultivating the Chlorella protothecoides cells heterotrophically in the dark further comprises limiting the availability of nitrogen.
 6. The edible microalalgal flour of claim 1, wherein the cells are cultivated at a pH of 4 to
 9. 7. The edible microalgal flour of claim 1, wherein high-temperature-short-time pasteurization process comprises heating the broth to a temperature of from 70° C. to 95° C. for 10 to 180 seconds.
 8. The edible microalgal flour of claim 1, wherein high-temperature-short-time pasteurization process further comprises immediately cooling the cells after heating.
 9. The edible microalgal flour of claim 1, wherein the washing and harvesting of the cells is carried out by centrifugation, filtration, or dialysis.
 10. The edible microalgal flour of claim 1, wherein the process further comprises adding a preservative to the cells of Chlorella protothecoides after subjecting them to the high-temperature-short-time pasteurization process.
 11. The edible microalgal flour of claim 10, wherein the preservative is sodium benzoate and/or potassium sorbate.
 12. The edible microalgal flour of claim 1, wherein the Chlorella protothecoides cells are lysed with a bead mill.
 13. The edible microalgal flour of claim 1, wherein the process further comprising homogenizing the Chlorella protothecoides cells before drying them.
 14. The edible microalgal flour of claim 1, wherein the process further comprises holding the lysed cells of Chlorella protothecoides at a temperature of 70° C. to 80° C. for 1 to 6 minutes before drying them.
 15. The edible microalgal flour of claim 1, wherein the lysed Chlorella protothecoides cells are dried using a spray dryer.
 16. The spray dryer of claim 15, wherein the spray dryer is a box dryer.
 17. The spray dryer of claim 15, wherein the spray dryer is a tall form dryer.
 18. The spray dryer of claim 15, wherein the spray dryer is a fluidized bed dryer.
 19. The edible microalgal flour of claim 1 having a lipid content between 40% to 60%.
 20. The edible microalgal flour of claim 1 having a pH between 5.5 and 8.5 when dissolved in water at 1% (w/v).
 21. The edible microalgal flour of claim 1 having a pH between 6.0 and 8.0 when dissolved in water at 1% (w/v).
 22. The edible microalgal flour of claim 1 having a pH between 6.5 and 7.5 when dissolved in water at 1% (w/v).
 23. The edible microalgal flour of claim 1 comprising less than 100 ppm of chlorophyll. 